The present invention relates generally to rotary lobe pumps. More particularly, the present invention relates to rotary lobe pump timing adjustment.
Rotary lobe pumps are used in industry for positive-displacement pumping of foodstuffs, pharmaceuticals, and other materials requiring avoidance of cross-contamination, freedom from chemical interaction with a wide range of substances, and good mechanical strength. Dimensional tolerances in all parts of the pumps, especially in the vicinity of the working lobes, are extremely close. Tight, uniform tolerances between the lobes of the two rotors and between the rotor tips and the walls of the pumping chamber are desirable because insufficient clearance results in binding and wear, while excessive clearance reduces pumping efficiency.
The requirements for strength, low contamination, and inertness lead to the use of 316 corrosion resistant (xe2x80x9cstainlessxe2x80x9d) steel (CRS), special alloys, or the like for parts exposed to the materials being pumped. Parts fabricated of such alloys can be sterilized and satisfy structural and producibility needs.
The two rotors comprising the materials-handling part of rotary lobe pumps are geared together with tight-tolerance spur gears, helical gears, or another low-lash, positive mesh design. Such pumps use rather long drive shafts between the materials-handling end and the drive end of the pump, ensuring dimensional stabilityxe2x80x94the long intermediate region housing the bearings holds the shafts rigidly parallel. Typical designs also provide a degree of thermal isolation, as well as physical separation between the materials-handling end and the drive end.
In food and drug applications, Federal and state regulations call for disassembly for cleanliness inspections and operational tests on the order of once per day to once per month for pumps in continuous use. Standard procedures in the user industries call for testing in place (removal of front cover, visual exam, shim test, and possible swab for culture) preceded and followed by a cleaning flush. If the shim test fails, the typical previous design of pump must be removed from the system, taken to a shop, and overhauled.
For previous designs, the rotors are keyed or otherwise rigidly attached to their shafts, while friction clamping on the gears at the drive end of the shafts fixes the rotational relationship, termed here the timing, between the shafts. For such designs, timing adjustment requires disassembly of piping and demounting of the pump, then removing access covers on the drive end for adjustment and on the materials-handling end for measurement. The adjustable gear clamp must be loosened, shims set in place between the rotor lobes, the assembly tightened again, and the workmanship checked by moving the shims to critical locations and rotating the shafts. Finally, the entire assembly must be lubricated, sterilized, and remounted to the machine from which it was removed.
Materials being pumped can contain foreign or oversized particles that migrate to the points of least clearance. Such obstructions can cause transient torque spikes to be applied between the two rotors or between the rotors and their driving mechanisms. This in turn can exceed the friction limits of the clamping devices, resulting in alignment shift. Unless the shift causes noticeable anomaliesxe2x80x94noise, slowing of drive motors, and the likexe2x80x94such errors ordinarily remain in the system until the next periodic servicing event.
Accordingly it is desirable to provide a rotary lobe pump that simplifies maintenance by leaving the drive end of the pump sealed during routine timing adjustment.
It is therefore a feature and advantage of the present invention to provide the capability to relocate the adjustment provision of rotary lobe pump timing to the materials-handling end of the pump.
It is another feature and advantage of the present invention to provide continuously adjustable timing through use of slotted, tapered bushings.
It is another feature and advantage of the present invention to permit routine maintenance with unimpaired precision while the pump remains in place on the machine of which it forms a part.
It is another feature and advantage of the present invention to have the ability to leave gear mesh at the drive end of the pump intact during pump lobe timing adjustment.
The above and other features and advantages are achieved by a novel method of fixing lobe pump rotors, as herein disclosed. In accordance with one embodiment of the present invention, a pump for pumping material comprises a first shaft, a first tapered bushing, sized to fit the first shaft, a first rotor, fitting the first shaft, with an internal tapered region fitted to the first tapered bushing, and a first threaded fastening device that urges the first rotor and the first shaft into frictional contact with the first bushing.
In another aspect, the invention provides apparatus for setting timing of rotors in a rotary lobe pump, comprising a tapered bushing; a rotor configured to mesh with an identical rotor in overlapping rotational paths; a shaft configured to accept the rotor; and means, such as a threaded fastening device, for securing the bushing, rotor, and shaft together.
In another aspect, the invention provides a method for providing adjustable timing of lobe pump rotors, comprising the steps of equipping each rotor with a tapered inner mating surface; equipping each rotor with a flat rear mating surface; driving each rotor with a drive shaft having a shoulder that mates to a flat rear mating surface of the rotor; locating a tapered bushing between at least one of the shafts and its respective rotor; and applying compression normal to the inner mating surface of the rotor to secure the bushing, rotor, and shaft together.
There have thus been outlined, rather broadly, the more important features of the invention in order that the detailed description thereof that follows may be better understood, and in order that the present contribution to the art may be better appreciated. There are, of course, additional features of the invention that will be described below and which will form the subject matter of the claims appended hereto.
In this respect, before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein, as well as the abstract, are for the purpose of description and should not be regarded as limiting.
As such, those skilled in the art will appreciate that the conception upon which this disclosure is based may readily be utilized as a basis for the designing of other structures, methods and systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention.